HID: ntrig: fix touch events

This reinstates the lost unpressing of BTN_TOUCH.  To prevent undesireably
touch toggles this also deals with tip switch events.

Added a trap to prevent going out of bounds for hidinputs with empty reports.

Clear bits of unused buttons which result in misidentification.

Signed-off-by: Rafi Rubin <rafi@seas.upenn.edu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>